Remote controlled aircraft, in particular for surveillance or inspection

ABSTRACT

The invention concerns a remote-controlled flying machine, in particular for surveillance and inspection, capable of hovering and comprising a spherical open-worked resistant shroud integral with a cylindrical fairing wherein rotates a propeller powered by an engine housed in a fuselage secured to the fairing with radial arms and straightening vanes.

[0001] The invention relates to a remote controlled aircraft or drone inparticular for surveillance or inspection, for example of works of art,suspended cables, high voltage power lines, nuclear installations, etc.

[0002] Such an aircraft is generally equipped with observation anddetection means, in particular a camera for producing images ofoverflown zones, allowing both visual inspection of the zones andallowing the aircraft to be piloted by sight, and a propeller or rotorwith a vertical axis allowing vertical takeoff and hovering.

[0003] Mounting the propeller in a cylindrical fairing has already beenproposed to slightly reduce the dimensions of the propeller for the samethrust and to reduce the risks of the rotating propeller impinging onsurrounding objects or personnel.

[0004] The invention aims to substantially improve that type of aircraftto enable it to be used in complete safety and to substantially improveits performance and versatility in service.

[0005] The invention also aims to provide such an aircraft that can takeoff and land substantially vertically, move in forward flight and hover.

[0006] To this end, the invention provides a remote controlled aircraftprovided with observation and/or detection means, a propeller with avertical axis rotating inside a substantially cylindrical fairing and anengine powering the propeller, characterized in that the centre ofgravity of the aircraft is located below its geometrical centre and inthat the assembly comprising the detection and/or observation means, theengine and the propeller is surrounded by a substantially sphericalopen-worked outer cage that is integral with the fairing.

[0007] By dint of these characteristics, the aircraft of the inventioncan take up a stable position on the ground in which the axis of thepropeller is substantially vertical. It can take off vertically, land onthe ground and automatically adopt its stable position, and take offagain vertically. Further, in the event of a shock to the aircraftagainst an obstacle, the outer cage protects the aircraft from damageand also protects the obstacle struck by the aircraft.

[0008] Advantageously, the outer cage is formed from at least onematerial that is light and shock resistant.

[0009] In one embodiment of the invention, at least a portion of thecage is formed as a single piece with the fairing and is preferablyformed from a closed cell plastics material such as a polyethylene foam.

[0010] In a variation, said cage is at least partially metallic andcomprises a grill or screen fixed or locked into the fairing.

[0011] In a further feature of the invention, the aircraft comprises anaxial fuselage the aft portion of which contains the engine and theobservation and/or detection means, and redressing vanes extending aftof the propeller between the fairing and the axial fuselage to preventthe aircraft from rotating about the axis of the propeller. In aparticularly simple embodiment of the invention, said redressing vanesare fixed. In a more sophisticated and expensive embodiment, saidredressing vanes can be orientated about an axis perpendicular to theaxis of the propeller and are controlled by servo-motors.

[0012] In a further characteristic of the invention, said aircraft alsocomprises control surfaces formed by flaps or ailerons which extend inthe aft portion of the aircraft between the fuselage and said cage andwhich can be orientated about axes perpendicular to the axis of thepropeller to direct the aircraft by rotation about its pitch, yaw and/orroll axes.

[0013] A control circuit comprises a microprocessor and optionally atleast one gyroscope that can determine the appropriate values for theengine speed and for the position of the redressing vanes and/or controlsurfaces as a function of the commands given by an operator (for exampleclimb or descend, move forward, turn to left or to the right, movebackwards).

[0014] In a first embodiment, the aircraft is equipped with an electricmotor and storage batteries, the latter being located inside the axialfuselage or carried by the fairing.

[0015] In a further embodiment, the aircraft is equipped with a heatengine and a fuel tank, the latter being located inside the axialfuselage or carried by the fairing.

[0016] The invention also envisages means for dynamic stabilisation ofthe aircraft in transitional motion, comprising a mobile mass-balanceweight mounted as an inverted pendulum on the axis of the propellerforward thereof. Elastically deformable return means and means fordampening the displacement are associated with said mobile weight.

[0017] Displacement of said mobile mass-balance weight is phase opposedwith any angular drift of the aircraft compared with a desiredtrajectory and can limit it and slow it sufficiently to correct itmanually or automatically.

[0018] The stabilisation means can be passive or active. In the lattercase, they are associated with servo-motors which can be controlledeither by an operator or automatically, for example using an inertialonboard navigation platform or a remote image treatment system, whichcan obtain references, in particular vertical references, from imagestransmitted by the observation means of the aircraft.

[0019] The aircraft of the invention can have a wide range of dimensionsdepending on the tasks it is intended to fulfil. Its design enables itto be produced with simple means that are commercially available at arelatively low cost.

[0020] The invention will be better understood and othercharacteristics, details and advantages will become apparent from thefollowing description made with reference to the accompanying drawingsin which:

[0021]FIG. 1 is a diagrammatic axial cross sectional view of an aircraftin accordance with the invention;

[0022]FIG. 2 is a diagrammatic axial cross sectional view of a variationof the aircraft;

[0023]FIG. 3 is a diagrammatic view of means for activating the controlsurfaces;

[0024] FIGS. 4 to 7 show diagrammatic cross sectional views ofvariations of the aircraft.

[0025] In the embodiment shown in FIG. 1, reference numeral 10designates a propeller of any type (twin blade, four-blade or the like)driven in rotation by an electric motor 12 advantageously associatedwith a variable rotation speed drive and powered by storage batteries14, the propeller rotating inside a cylindrical fairing 16 which iscoaxial with the propeller.

[0026] Engine 12 and storage batteries 14 are arranged axially inside afuselage 18 of truncated conical shape which extends from the boss 20 ofthe propeller to the aft end 22 of the aircraft which is equipped withcontrol surfaces 24.

[0027] The fuselage 18 is extended beyond propeller boss 20 by a dome 26in the form of a half-ellipsoid connected to fairing 16 via radial arms28 extending in front of the propeller. Redressing vanes 30 extendradially aft of propeller 10 and connect fairing 16 and fuselage 18;propeller 10 can turn freely between the arms 28 and redressing vanes30.

[0028] The rear portion 22 of the fuselage is used to house servocontrol circuits 32 for the engine 12, the control surfaces 24 andoptionally the redressing vanes, as will be described in detail below,and also houses observation and detection means 34 comprising, forexample, at least one video camera, a microphone and one or more sensorsof a variety of types.

[0029] Control surfaces 24 in this embodiment are formed by four flapsdistributed at 90° with respect to each other about the axis of thepropeller and pivotally mounted on portion 22 of the fuselage about axes36 that are perpendicular to the axis of the propeller.

[0030] Similarly, redressing vanes 30 can be pivotally mounted about anaxis perpendicular to the axis of the propeller, their position beingadjusted to stabilise the aircraft and prevent it from turning about thepropeller axis when the latter is driven in rotation.

[0031] In a variation, the redressing vanes are fixed and theirinclination is adjusted to suit the nominal rotation speed of thepropeller.

[0032] The dome 26 contains radio circuits 37 communicating with groundmeans and comprises an axial antenna 38 for transmitting informationsupplied by observation and detection means 34 and for receiving controlsignals sent by an operator on the ground.

[0033] A substantial spherical cage 40 completely surrounds the aircraftdescribed above and is fixed to the fairing 16 via studs or an annularstrip 42 of elastically deformable plastic foam, rubber or elastomerwhich can absorb shocks and vibrations.

[0034] This spherical cage 40 is connected to the lower portion 22 ofthe fuselage via a ring 44 of the material described above, mountedaround the observation and detection means 34 to protect them fromshocks.

[0035] Cage 40 is substantially open-worked and is formed, for example,by a grid or screen of light metal that is shock resistant, which canadvantageously be connected to axial antenna 38 and itself form anantenna.

[0036] In this assembly, the centre of gravity of the aircraft is belowthe geometrical centre and above the centre of aerodynamic thrust of theaircraft, so that it can take up a stable position on the groundcorresponding to that shown in FIG. 1, the axis of the propeller beingvertical.

[0037] This aircraft can be used as follows:

[0038] Using a remote control of a commercially available type as usedfor model aeroplanes, for example, an operator can send piloting ordersthat are captured by antenna 38 and optionally 40 and transmitted toservo-control circuits 32 to control the power to the propeller fromelectric motor 12 and regulate its rate of rotation (via the electronicvariable drive), optionally regulating the inclination of the redressingvanes 30 to prevent the aircraft from rotating about the propeller axis,and to control displacement of the aircraft in a given direction bymeans of control surfaces 24 which cause the aircraft to pivot about itspitch, yaw and/or roll axes. Means that will be described in detailbelow can dynamically stabilise the aircraft by limiting and slowing itstransitional movements about its centre of gravity, so that they can becorrected either manually or automatically.

[0039] In one embodiment, the servo-control circuits 32 comprise one ormore on-board gyroscopes associated with a microprocessor which may ormay not be on-board to provide reference positions for the redressingvanes 30 and control surfaces 24.

[0040] Using the remote control, the operator can make the aircraft takeoff vertically when it is on the ground in its position of stableequilibrium corresponding to that of FIG. 1, then the operator can steerthe aircraft in any direction to carry out surveillance and inspectionoperations, for example.

[0041] The images recorded by the video cameras or cameras comprisingpart of the observation and detection means 34 are transmitted to theground via radio connection circuits 37 and are displayed on atelevision type screen or on special spectacles to be visible to theoperator who can then pilot the aircraft by sight as though the operatorwere in the aircraft. As an example, type PLM-A35 or PLM-S700 spectaclessold by SONY could be used, which provide the operator with a panoramicvision from the aircraft. When the operator turns his head, the field ofvision on the spectacles turns in the same manner as though the operatorwere on board the aircraft. Advantageously, the panoramic image issupplied via arrays of photodetecting diodes (line camera). By rotatingthe aircraft about a vertical axis, keeping within piloting limits, animage is obtained of all or part of the ground to be observed over 360°.The use of a line camera for this purpose is known to the skilledperson.

[0042] The spherical cage 40 protects the aircraft from any interferencewith the external environment and also protects this environment fromrisks of damage by propeller 10. This cage 40 means that the operatorcan put the aircraft on the ground allowing it to fall either gently orharshly from a relatively low height, then the aircraft can take offagain vertically, as the aircraft on the ground is automatically broughtinto its stable equilibrium position because its centre of gravity islocated below its geometrical centre.

[0043] In one particular embodiment, the external diameter of cage 40 is180 to 200 millimeters, the weight of the aircraft is of the order of350 grams, the diameter of the propeller is 152 millimeters, theelectric motor 14 and the storage batteries provide a driving force ofthe order of 30 watts and a thrust of the order of 4N, the flying rangeis of the order of 5 minutes and the aircraft can reach an altitude of afew hundred meters.

[0044] Clearly, the dimensions of the aircraft can be varied upwardly ordownwardly within wide limits, and it is also possible to substantiallyincrease its flying range by replacing the electric motor 12 and storagebatteries 14 with a reciprocal or rotary piston engine associated with afuel tank, giving it a flying range of a few tens of minutes.

[0045] As already indicated, observation means 34 can comprise at leastone video camera associated with an emitter for transmitting images tothe ground. Suitable camera-emitter ensembles are commercially availableand weigh of the order of 65 to 70 grams.

[0046] In a variation shown diagrammatically in FIGS. 2 and 3, fairing16, control surfaces 24, connecting arms 28, redressing vanes 30 andouter cage 40 are formed from a closed cell plastics material that islight and shock resistant such as a polyethylene foam with a density ofthe order of 25 to 35 kilos per cubic meter, or the like.

[0047] In this case, cage 40 is not constituted by a screen or grid butby spindles which extend either side of a continuous annular stripforming the fairing 16.

[0048] The assembly formed by fairing 16, control surfaces 24, arms 28,redressing vanes 30 and cage 40 is formed by injection moulding twohemispherical portions that are connected together along a joint planethat is perpendicular to the axis of propeller 10 at the fairing 16, asindicated by dotted line 46, for example.

[0049] Redressing vanes 30 are fixed and are extended aft by flapsforming control surfaces 24 to which they are connected by flexiblehinges formed by local necks 48 as shown diagrammatically in FIG. 3.

[0050] Each flap 24 pivots about flexible hinge 48 by means of aservo-motor (not shown) housed inside fairing 16 or fuselage 18 theoutlet shaft of which comprises crossed arms 50 connected via lines 52to a crossbar 54 that is integral with flap 24 and located on the otherside of the hinge 48 with respect to arms 50, so that rotation of arms50 pivots flap 24 about hinge 48, as shown in dotted lines in FIG. 3.These flaps 24 have relatively large dimensions and act as a wing whenthe aircraft is in forward flight.

[0051] In general, it is advantageous to reduce the thickness of arms 28and redressing vanes 30 in a plane perpendicular to FIGS. 1 and 2 toreduce pressure drops and thus power losses.

[0052] Tests have shown that arms 28 with a shape corresponding to thatshown in the drawings also act as redressing vanes, complementing theredressing vanes 30, which can be fixed and have a cross section asshown in FIG. 2, to recover a portion of the thrust of the propeller andredress the airflow.

[0053] In a variation, arms 28 can be replaced by filamentary elementsthat form part of cage 40, which can further reduce pressure drops andpower losses.

[0054] In the embodiment shown in FIG. 2, storage batteries 14 supplyingengine 12 are no longer in fuselage 18 but are inside fairing 16 anddistributed uniformly about the axis of the aircraft.

[0055] As shown in FIG. 2 in dotted lines, the foam plastic material canform an axial tube 56 forward of the propeller between cage 40 and thefront portion 26 of the fuselage, and antenna 38 is located inside thattube 56.

[0056]FIG. 4 diagrammatically shows an embodiment of the means citedabove for dynamic stabilisation of the aircraft in transitional motion.In this example, which corresponds to the embodiment of FIGS. 2 and 3, amobile mass-balance weight 60 is mounted as an inverted pendulum on theforward portion of the aircraft in the axis of the propeller and isconnected to dome 26 via a rod 62 forming a spring operating as a leafspring.

[0057] In this configuration, the length of bendable rod 62 is selectedso that the distance between the point at which it is fixed to dome 26and the centre of gravity of the mass-balance weight 60 is equal to thedistance between that fixing point and the centre of gravity of theaircraft. The value of the mobile weight and the stiffness of thebendable rod are determined so that the oscillations of the mobileweight 60 are synchronous and in phase opposition with those of theaircraft about its centre of gravity.

[0058] When an angular drift occurs, which causes the aircraft to pivotabout its centre of gravity and which is due to the fact that the thrustpassing through the centre of thrust is angularly offset with respect tothe axis of the aircraft and no longer passes through the centre ofgravity, pivoting the mobile weight 60 with respect to its point offixing to dome 26 as a result of inertia effects tends to limit and slowthe pivoting of the aircraft about its centre of gravity. The angulardrift of the aircraft about its centre of gravity is thus sufficientlylimited and decelerated for it to be able to be corrected either usingthe remote control or automatically.

[0059] To this end, a number of solutions are possible:

[0060] the aircraft can be provided with an inertial navigation platformwhich will provide set positional values for control surfaces 24 tocancel and compensate for the angular drift of the aircraft about itscentre of gravity;

[0061] a remote system for treating images can receive images taken bythe video camera or cameras in the aircraft, seek out reference pointssuch as horizontal or vertical lines and produce corrective signalswhich are transmitted to the control surfaces' servo-motors 24.

[0062] Displacement dampening means are associated with the mobileweight 60. Advantageously, they are constituted either wholly orpartially by a component of the aircraft equipment, for example itsradio receiver, so as not to increase the onboard weight. Wires 64connecting the radio receiver to the dome 26 can form the dampeningmeans mentioned above or can form part thereof.

[0063] In a variation, the mobile mass-balance weight 60 can be mountedat the end of an axial tube 66 formed from a deformable elastic materialsuch as the plastics material foam constituting cage 40, fairing 16 andradial arms 28. This tube 66 of deformable elastic material can beintegral with the radial arms 28, thus replacing bendable rod 62. Thedimensions of tube 66 are determined as a function of the desiredbending stiffness of the bendable rod.

[0064] In a further variation shown diagrammatically in FIG. 5, mobileweight 60 is slidably mounted on rod 62 and is supported by a spring 67which is a compression spring in the example shown and which can varythe length of the inverted pendulum formed by weight 60 and rod 62 inaccordance with the law m.γ.l=a constant, m being the mass of the mobileequipment, γ the applied acceleration and l the length of the pendulum.Spring 67 enables this length to be automatically varied as a functionof the thrust and thus to automatically adapt the dynamic stabilisationmeans to variations in thrust. An adjustable abutment at the end of rod62 defines the maximum length of the pendulum. Advantageously, rod 60 ismounted on the fairing or on the fuselage by means of a damped pot-typejoint and adjusting screws are provided to define an initial positionfor rod 62 corresponding to placing the centre of gravity of theaircraft on the thrust axis, adjustment being carried out in theworkshop on a test rig following assembly of the aircraft to compensatefor any imbalance.

[0065] In a further embodiment, the means for dynamic stabilisation ofthe aircraft in transitional motion are active. To this end,servo-motors are associated with support 62 or 66 of the mobilemass-balance weight 60 to provide a desired angular position withrespect to the axis of the aircraft. These servo-motors are controlledeither by the operator using the remote control, or automatically usingan inertial navigation platform or a remote image treatment system, asindicated above.

[0066] In the variation shown in FIG. 6, fairing 16 is formed from acomposite material, for example based on carbon fibres, and comprisestwo coaxial cylindrical skirts 68 and 70 respectively connected togetherby redressing vanes 30. Cage 40 can then be formed from two half-shellsnested on the fairing 16, the forward half-shell comprising the radialarms 28 defined above.

[0067] In the embodiment shown in FIG. 7, fairing 16 and redressingvanes 30 are formed from a single piece of foam plastics material,optionally with flaps 24 to which they are connected via flexible hinges48. Cage 40 is then formed from two substantially hemispherical coversof metal wire shown as dotted lines, and these covers are easily fixedby locking onto fairing 16, the corresponding ends of the metal wiresbeing bent back at right angles to form points that are buried in thematerial of the fairing 16.

[0068] In general, the aircraft of the invention performs completelysatisfactorily in the air. When equipped with dynamic stabilisationmeans as described above, it is possible to use it both for verticallanding and takeoff, for hovering and to put into forward flight. Whenequipped with an electric motor, it has a relatively short flying rangebut it is silent, it can be landed at any suitable location and can takeoff again from that location, under remote control. When equipped with aheat engine, it has a longer range and better performance in the air,but it is harder to land it and make it take off remotely.

1. A remote controlled aircraft, in particular for surveillance andinspection, provided with observation and/or detection means (34), apropeller (10) with a vertical axis rotating inside a substantiallycylindrical fairing (16) and an engine (12) powering the propeller,characterized in that the centre of gravity of the aircraft is locatedbelow its geometrical centre and in that the assembly comprising thedetection and/or observation means, the engine and the propeller issurrounded by a substantially spherical open-worked outer cage (40) thatis integral with the fairing.
 2. An aircraft according to claim 1,characterized in that the cage (4) is formed from at least one materialthat is light and shock resistant.
 3. An aircraft according to one ofthe preceding claims, characterized in that at least a portion of thecage (40) is formed as a single piece with the fairing
 4. An aircraftaccording to one of the preceding claims, characterized in that at leasta portion of the cage (40) is formed from a closed cell plasticsmaterial such as a polyethylene foam.
 5. An aircraft according to one ofclaims 1 to 4, characterized in that at least a portion of the cage (40)is metallic and comprises a grill or screen.
 6. An aircraft according toone of the preceding claims, characterized in that it comprises an axialfuselage (18) the aft portion of which contains at least one engine (12)and the observation and/or detection means (34), and redressing vanes(30) extending aft of the propeller between the fairing (16) and theaxial fuselage (18).
 7. An aircraft according to claim 6, characterizedin that said redressing vanes (30) are fixed or can be orientated aboutan axis perpendicular to the axis of the propeller and controlled byservo-motors.
 8. An aircraft according to one of the preceding claims,characterized in that it comprises control surfaces formed by flaps orailerons (24) which extend in the lower portion of the aircraft insidesaid cage and which can be orientated about axes (36) perpendicular tothe axis of the propeller to direct the aircraft by rotation about itspitch, yaw and/or roll axes.
 9. An aircraft according to one of claims 6to 8, characterized in that the axial fuselage (18) comprises a forwardportion in which equipment such as radio connection means (37) arehoused, and radial arms (28) connecting the forward portion of thefuselage to the fairing (16) forward of the propeller (10).
 10. Anaircraft according to one of claims 6 to 9, characterized in that it isequipped with a heat engine and a fuel tank or with an electric motor(12) and storage batteries (14), the tank or storage batteries beinghoused in the axial fuselage (18) or carried by the cylindrical fairing(16).
 11. An aircraft according to one of claims 1 to 10, characterizedin that it comprises means for dynamic stabilisation of the aircraft intransitional motion comprising, forward of the aircraft, a mobilemass-balance weight mounted as an inverted pendulum on the axis of thepropeller, elastically deformable return means for the mobile weight andmeans for dampening the displacement of said mobile mass.
 12. Anaircraft according to claim 11, characterized in that the length of theinverted pendulum varies as a function of the acceleration, the mobilemass being slidably mounted on a bendable rod, for example, whichconnects to the aircraft and is supported by a spring regulating theposition of the mobile weight on said rod as a function of theacceleration.
 13. An aircraft according to claim 11, characterized inthat it comprises servo-motors for displacing the mobile weight,controlled by the operator.
 14. An aircraft according to claim 11,characterized in that said dynamic stabilisation means are automaticallycontrolled by an onboard inertial navigation platform or by a remoteimage treatment system that can produce references, for example verticalreferences, from images transmitted by the aircraft.